Process and composition for cleaning and coating metal surfaces



United States Patent 3,484,304 PROCESS AND COMPOSITION FOR CLEANING AND COATING METAL SURFACES James R. Beach, Detroit, Mich., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed Oct. 11, 1966, Ser. No. 585,746

, Int. Cl. C23f 7/10 US. Cl. 1486.15 6 Claims ABSTRACT OF THE DISCLOSURE An iron phosphate cleaner-coater composition for treating ferrous metal surfaces, which composition includes an alkali metal acid pyrophosphate, an alkali metal phosphate, ferric iron ions, a low foaming Wetting agent and p-nitrobenzoic acid.

This invention relates to a novel composition and process for cleaning and coating metal surfaces and more particularly, it relates to a process and composition suitable for cleaning ferrous metal surfaces while simultaneously forming a phosphate coating on the surface being cleaned.

It has long been the practice in the art to treat metal surface to form a protective phosphate or similar coating on a metal surface. Frequently, zinc phosphate or mixed zinc-iron phosphate coatings have been used because of the excellent corrosion resistant, paint-base coatings they provide. Often, however, the high degree of corrosion protection provided by such phosphate coatings is not required. This has been found to be particularly true where the treated metal is used in application in which resistance to salt spray is not an important factor. In such instances, the added cost of the zinc phosphate and mixed zinc-iron phosphate coatings is often difficult to justify, notwithstanding the improved corrosion protection which they provide.

It has, therefore, become the practice to utilize coating materials which produce an iron phosphate coating on the metal surface for many of these applications. T ypically, the surfaces treated are iron or steel surfaces and the coating compositions are aqueous solutions containing an alkali metal phosphate. Although the corrosion resistance of such coatings is not as great as that obtained from the Zinc phosphate coatings, the costsavings obtained more than make up for this difference, particularly where salt spray corrosion is not a problem. Although coatings of this type have generally been found tobe quite satisfactory for the purpose intended, some problems have been encountered both with respect to the application of the coating material and the properties of the. coating obtained.

One of the difficulties which has heretofore been encountered is that of producing a substantially dust-free coating. Additionally, coating solutions of this type frequently require a relatively close control of the process operating conditions and have been useful only over a relatively narrow pH range. Moreover, coatings of this type, which have been produced by the prior art processes, have often been unattractive, from a visual standpoint, thus detracting from their salability.

It is, therefore, an object of the present invention to provide an improved coating composition for producing a visually attractive, dust-free iron phosphate coating on metal surfaces.

Another object of the present invention is to provide an improved coating composition which is effective in cleaning the metal surface to remove dirt, oil, and other light soil from the metal surface during the coating operation.

A further object of the present invention is to provide an improved process for forming an iron phosphate coating on the metal surfaces, which process is easily controlled and may be operated at a relatively low temperature, over a relatively Wide pH range.

These and other objects will become apparent to those skilled in the art from a description of the invention which follows.

Pursuant to the above objects, the present invention includes a cleaning-coating concentrate composition which comprises an alkali metal acid pyrophosphate, an alkali metal phosphate, ferric iron ions, a low-foaming wetting agent, and p-nitro benzoic acid. When iron or steel is treated with an aqueous solution formed from this concentrate, oil, grease and other similar light surface soils are removed from the metal and there is formed thereon an attractive, dust-free iron phosphate coating.

More specifically, in the practice of the present invention, the cleaner-coater concentrate is comprised of an alkali metal acid pyrophosphate (M I-I P Or -Where M is an alkali metal) and an alkali metal phosphate selected from the group consisting of mono-, cli-, and tri-, alkali metal phosphates. It is to be appreciated, that as used in the specification and claims, the term alkali metal is intended to refer to sodium, potassium, lithium, cesium, and rubidium. Of these, the preferred alkali metal is sodium and, for this reason, specific reference will be made hereinafter to this material. This is not, however, to be taken as a limitation of the present invention since other alkali metals are also useful and the phosphates and pyrophosphates of these, as well as sodium compounds, alone or in admixture, may be used in the present composition and process.

Of the alkali metal acid pyrophosphates and alkali metal phosphates indicated hereinabove as being useful in the composition of the present invention the preferred alkali metal acid pyrophosphate is sodium acid pyrophosphate and the preferred alkali metal phosphate is monosodium phosphate. Desirably, the alkali metal acid pyrophosphate and the alkali metal phosphate are present in the composition in a combined amount of at least 50% by weight of the concentrate composition. Combined amounts of the alkali metal acid pyrophosphate and alkali metal phosphate Within the range of about 50 to about 96% by weight of the concentrate composition are typical, with amounts within the range of about to about 92% by Weight of the concentrate composition being preferred. Desirably, the weight ratio of alkali metal acid pyrophosphate to the alkali metal phosphate is Within the range of about 1:1 to 15:1, with Weight ratios Within the range of about 3:1 to 10:1 being preferred.

The ferric iron ions may be added to the present composition as various ferric iron compounds which are dispersible and/ or soluble in Water. Examplary of such compounds which may be used are ferric sulfate, ferric nitrate, ferric chloride, ferric ammonium citrate, ferric oxalate, and the like. Typically, the ferric ions calculated as ferric sulfate are present in the composition in an amount within the range of about 0.1 to 4% by Weight of the concentrate composition, with amounts within the range of about 0.2 to 3% by weight of the composition being preferred.

The low foaming Wetting agent is desirably present in the cleaner-coater concentrate composition in an amount within the range of about 1 to 12% by weight of the composition and preferably constitutes about 2 to 9% by weight of the composition. Although various wetting agents of the low foaming type, including anionic, cationic, and nonionic Wetting agents may be used, the nonionics are generally preferred, with the biodegradable forms of these wetting agents being the most preferred.

The wetting agents may be of various types, such as fatty esters, sulfates, aliphatic polyethers, polyoxyethylene esters of fats and oils such as vegetable oils, organic polyphosphate esters, amine salts of alkyl aryl phosphates, polyglycol fatty acid esters, alkyl phenolpolyglycol ethers, modified amines, alkyl aryl sulfonates, amine polyglycol condensates, alkyl arylpolyethers, ethoxylated tall oil, polyoxyethylene ethers, alkyl polyethylene oxide alcohols, and the like, as are known in the art. Typically, in these materials the aryl group is phenyl or naphthyl, the alkyl group contains from about 2 to 20 carbon atoms and when alkoxylated, they contain from about 2 to 15 moles of the alkylene oxide, such as ethylene oxide or propylene oxide.

In addition to the above components, the cleaner-coater concentrate composition of the present invention also contains p-nitro benzoic acid. Desirably, this material is present in the concentrate composition in an amount within the range of about 0.5 to about 10% by weight of the concentrate and preferably in an amount within the range of about 2.0 to about 6.0% by weight.

In formulating the working solution for treating iron and steel surfaces, in accordance with the method of the present invention, the concentrate composition is dissolved or dispersed in water so as to provide a working solution having the desired concentration. Typical concentrations that may be used are within the range of about 1 to about 25 pounds of the concentrate per 100 gallons of working solution with concentrations within the range of about 3 to about 18 pounds per 100 gallons of working solution being preferred.

The iron and steel surface to be treated is contacted with this aqueous solution for a period of time sufficient to effect cleaning of the surface and the formation thereon of the desired iron phosphate coating. Desirably, the treating solution is sprayed onto the metal surface although other contacting techniques, such as immersion and the like, may also be used. Typical contact times, when using spray application, are from about 5 seconds up to about 5 minutes, with contact times within the range of about 0.5 to 2 minutes being preferred. Although it is preferred that the treating solution be used at a temperature within the range of about 50 to 70 centigrade, in many instances, temperatures from about room temperature up to just below the boiling point of the working solution, e.g. 95 centigrade., may be used.

In carrying out the process of the present invention, the iron and steel surfaces to be treated are contacted with an aqueous treating solution as has been described hereinabove. In view of the ability of such treating solutions to remove oil, grease and similar light soil from the metal surface being treated, a separate cleaning step prior to the application of the treating solution is normally not necessary. Where, however, the surface to be treated contain oxide coatings, carbonaceous smut, or similar difficultly removable materials, an alkaline or acid precleaning step may be used. Following the contact of the metal surface with the treating solution, the thuscoated surface is desirably rinsed with water, preferably hot water at a temperature above about 50 centigrade. Rinsing times of from about seconds to about 2 minutes are typical with times within the range of about 0.5 to 1 minute being preferred. Thereafter, if desired, the water-rinsed surface may be given a further rinse, preferably with a dilute solution containing hexavalent chromium. Such solutions may contaian from about 0.03 to about 0.8 percent hexavalent chromium, calculated as CrO These solutions may be dilute chromic acid solutions or solutions of alkali metal or ammonium chromates and dichromates as well as dichromates of other metal, such as zinc, calcium, chromium, ferric iron, magnesium, aluminum or the like. The rinse solution may be used at room temperature or at an elevated temperature, temperature and times above about 55 centigrade and from 10 seconds to 2 minutes being typical with temperatures and times within the range of about 60 to degrees centigrade and 0.5 to 1 minute, respectively, being preferred. After drying the thus-rinsed surface, either at room temperature or at an elevated temperature sufficient to drive off surface moisture, e.g., to 200 degrees centigrade, the surface may be given a suitable protective coating, such as a paint, lacquer, or the like.

By the process of the present invention there is provided a simple and economical treatment for iron and steel surfaces which provides a uniform, dust-free, iron phosphate coating which has an attractive color and which provides an excellent base for paints and other protective coating materials. It has been found that the coating produced permits excellent coverage with only a low film thickness of most paints. Additionally, the process is easily controlled so that effective coatings are produced over a wide range of pH and tempertaures. Moreover, mild steel or black iron equipment can be used with only a minimum amount of sludge formation.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. It is to be appreciated that these examples are intended to be exemplary of the compositions and processes which may be used and are not to be taken as a limitation thereof. In these examples, unless otherwise indicated, temperatures are given in degrees centigrade and parts and percent are by weight.

EXAMPLE 1 A concentrate composition was formulated containing the following components in the amounts indicated.

Components: Parts by weight Sodium acid pyrophosphate 78 Monosodium phosphate 10 p-Nitrobenzoic acid 3 Ferric sulfate .9H O 2 Low foaming biodegradable wetting agent (straight chain aliphatic polyether formed by ethoxylation of oxyalcohol) 7 An aqueous treating solution was formulated by dissolving the above concentrate in water to form a solution containing nine pounds of concentrate per 100 gallons of treating solution. This solution at a temperature of about 60 centigrade Was sprayed for one minute on 4 x 12", 24 gauge cold rolled steel panels, having a light oil coating. Thereafter, the panels were rinsed for 30 seconds in hot water, immersed for 30 seconds in a dilute aqueous solutionof chromic acid containing 0.033 by weight C10 at about 20 centigrade. The panels were then dried in an oven at about 190 centigrade. The coating weight on the panelstreated was found to be about 0.016 to 0.023 gram per square foot and the coating was an attractive dust-free iron phosphate. Thereafter, a commercial alkyd paint was applied to the phosphate coated panels and thepanels were subjected to the 100% humidity, conical mandrel and impact physical test and the knife blade adhesion test. After 504 hours in the 100% humidity test, the panels had a rating of 10 while in the conical mandrel, mechanical impact, convex and knife adhesion tests, ratings of N, N and 10, respectively, were obtained. It is to be noted, that in the humidity and knife adhesion tests, the rating is on a scale of 0 to 10, 0 indicating poorest performance and 10 indicating best performance. In the conical mandrel and impact tests, the panels are rated with N (nil) when they are perfect, with no fracture or peeling ofthe paint.

, EXAMPLE 2 The procedure of Example 1 was repeated with the exception that working solutions were made up from the concentrate in amounts of 3, 6, 9,12, 15 and 18 pounds per 100 gallons of working solution, solutions were applied byspraying at times of 30, 60, 90 and seconds using solution temperatures of 38, 50, 60 and 72 degrees centigrade. In all instances, the panels treated were found to have a uniform, dust-free coating which was attractive in appearance and which gave test results comparable to the panels of the preceding example.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention as changes therewithin are possible and it is intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A concentrate composition useful in forming an aqueous solution for treating metal surfaces which consist essentially of an alkali metal acid pyrophosphate, an alkali metal phosphate, the alkali metal acid pyrophosphate and alkali metal phosphate being present in the composition in a combined amount within the range of about 50 to 96% by Weight, ferric iron ions, calculated as ferric sulfate, in an amount within the range of about 0.1 to 4% by weight, a low-foaming wetting agent in an amount within the range of about 1 to 12% by weight, and p-nitrobenzoic acid in an amount Within the range of about 0.5 to 10.0% by weight, the weight ratio of the alkali metal acid pyrophosphate to the alkali metal phosphate being within the range of about 1:1 to 15: 1.

2. The composition as claimed in claim 1 wherein the alkali metal acid pyrophosphate is sodium acid pyrophosphate and the alkali metal phosphate is mono-sodium phosphate.

3. An aqueous solution useful in treating metal surfaces to provide a protective and/ or paint-base coating thereon which consists essentially of water and, a concentrate composition as claimed in claim 1, said concentrate composition being present in the treating solution in an amount withinthe range of about 1 to 25 pounds per hundred gallons of treating solutions.

4. The aqueous treating solution as claimed in claim 3 wherein the alkali metal acid pyrophosphate is sodium acid pyrophosphate and the alkali metal phosphate is mono-sodium phosphate.

5. A method for treating ferrous metal surfaces to provide a protective and/or paint base coating thereon which comprises contacting the surface to be treated with the aqueous treating solution as claimed in claim 3 and maintaining the solution in contact with the surface for a period sufficient to form the desired coating thereon.

6. The method as claimed in claim 5 wherein the concentrate composition in the aqueous treating solution, the alkali metal acid pyrophosphate is sodium acid pyrophosphate and the alkali metal phosphate is mono-sodium phosphate.

References Cited UNITED STATES PATENTS 2,067,007 1/1937 Darsey 148-6.15 2,856,322 10/1958 Parson et al 1486.15 2,891,884 6/1959 Rausch et a1 1486.15 2,987,428 6/1961 Heller et al. 1486.15 3,060,066 10/1962 Ross et al 1486.1S

FOREIGN PATENTS 566,094 12/ 1944 Great Britain.

RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 134-4 

